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 A228550 Triangular array read by rows: T(n,k) is the number of simple labeled graphs with n vertices and k components such that each vertex has even degree; n >= 1, 1 <= k <= n. 2
 1, 0, 1, 1, 0, 1, 3, 4, 0, 1, 38, 15, 10, 0, 1, 720, 238, 45, 20, 0, 1, 26614, 5145, 868, 105, 35, 0, 1, 1858122, 215355, 21000, 2408, 210, 56, 0, 1, 250586792, 16797942, 980371, 64260, 5628, 378, 84, 0, 1, 66121926720, 2509697144, 84370230, 3306415, 163800, 11676, 630, 120, 0, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,7 COMMENTS The Bell transform of A033678(n+1). For the definition of the Bell transform, see A264428. - Peter Luschny, Jan 17 2016 LINKS Alois P. Heinz, Rows n = 1..45, flattened FORMULA E.g.f.: (A(x) + 1)^y, where A(x) = Sum_{n>=1} 2^C(n-1,2) * x^n/n!. Row sums are 2^binomial(n-1,2) = A006125(n-1). Column 1 is A033678 (because a connected graph has only one component). EXAMPLE T(3,1) = 1 counts the complete graph on 3 labeled vertices. T(3,3) = 1 counts the empty graph (no edges) on 3 labeled vertices. Triangular array T(n,k) (with rows n >= 1 and columns k = 1..n) begins: 1; 0, 1; 1, 0, 1; 3, 4, 0, 1; 38, 15, 10, 0, 1; 720, 238, 45, 20, 0, 1; ... MATHEMATICA nn = 8; e = Sum[2^Binomial[n - 1, 2] x^n/n!, {n, 1, nn}]; Prepend[Drop[Map[Insert[#, 0, -2] &, Map[Select[#, # > 0 &] &, Range[0, nn]! CoefficientList[ Series[(e + 1)^y, {x, 0, nn}], {x, y}]]], 2], {1}] // Grid PROG (Sage) # uses[bell_matrix from A264428] # Adds a column 1, 0, 0, 0, ... at the left side of the triangle. bell_matrix(lambda n: A033678(n+1), 9) # Peter Luschny, Jan 17 2016 CROSSREFS Cf. A006125, A033678, A264428. Sequence in context: A073234 A123685 A124917 * A354520 A189916 A025278 Adjacent sequences: A228547 A228548 A228549 * A228551 A228552 A228553 KEYWORD nonn,tabl AUTHOR Geoffrey Critzer, Aug 27 2013 STATUS approved

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Last modified February 5 20:57 EST 2023. Contains 360087 sequences. (Running on oeis4.)